Electric Light Bulb Question

good, now I can sleep tonight

The fan may be causing a voltage drop that lowers the bulb temperature.

The fan blades are blocking a portion of the light! If you put something that's not transparent in front of the bulb, like a fan blade, you can't see the light.

My wife wants to know why the car wheels in commercials sometimes turn counterclockwise when the car is moving forward. It's the same affect - stroboscopic.

pc-

As several other have said, it is due to the stroboscopic effect. To see a more dramatic example of this, if you have a variable speed fan or at least a 3 speed fan, you can make the fan stop with ordinary household items. The light will again be dimmer but the fan will stop.

Turn off all the incandescent, LED's, halogen in the area and the fan. Take a fluorescent light and shine it on the fan, doesn't have to been extremely close. Turn the fan on, if variable speed, and increase the fan speed slowly up until the fan image stops jumping around. You may be able to see the fan blades in several positions if done slowly. When you see the same number of fan blades that the fan actually has, it is rotating at a multiple of 120. This is due to the fluorescent lamp putting out 120 short flashes per second (60 Hertz *2). Each flash starts quickly and ends quickly. Increase the fan speed and the fan image will jumble up until the fan is operating at another harmonic of the lamp.

This is the principle of how light (or flashing) style tachometers work. It is also very helpful to find vibrations and their frequencies and variations in speed.

An incandescent lamp is a constant illumination. For Direct Current the power goes through the tungsten element and heats it up which causes it to glow. For AC the same is done since the tungsten element doesn't have enough time to cool down. Each pulse of electricity from the AC in the form of the sine wave of the power doesn't give the element time to cool down.

If the fan is 3 speed try it between speed settings, You may also see it with that.

Good Luck, Old Salt

I understand the stroboscopic effect on the fan, but the OP was not asking about the fan...he asked "why do we see the electric bulb glowing slowly...".

Tom Consulting-

Op stated, "why do we see the electric bulb glowing slowly when seen through a revolving fan?"

The first paragraph of the reply was address as a method of making this effect more noticeable without extensive laboratory equipment, only ordinary household items.

As several other have said, it is due to the stroboscopic effect. To see a more dramatic example of this, if you have a variable speed fan or at least a 3 speed fan, you can make the fan stop with ordinary household items. The light will again be dimmer but the fan will stop.

Unless I am mistaken, the OP was asking why do we see the electric bulb glowing dimmer as the fan rotated at a faster speed or as to why it was dimmer with the fan rotation compared to the fan not rotating.

This was the principle during the 80's for "Disco Lights".

Unless I am mistaken, the answer was directed directly and correctly to the OP.

Good Luck, Old Salt

probably my age again... kicks in at the worst times now!

I completely understand that it is due to stroboscopic effect.

Thanks to all.

But, there is one doubt. Suppose the frequency of the electricity is 50 Hz and I see this dimming effect, then does that mean, the fan is rotating faster or slower compared to electricity frequency (3 blade fan).

Please note that I am asking about dimming effect not On and Off. That means the light slowly goes off and slowly goes on, approximately 1 sec interval "when seen through a revolving fan".

I think the same phenomenon is responsible in old movies wherein a TV (CRT screen) set inside the movie always has this black line going up or down. Something to do with the frequency of CRT screen and frequency at which the film shots are taken.

You need to understand that an incandescent light bulb is "off" twice, during each cycle of the AC current.

Frequency of the source isn't important. It's the position of the fan blades, in front of the source during the cycle.

If the bulb were somehow covered by blades at all times, except when the cycle was at exactly the midpoint, the light would be "out" completely. Look at a sine wave of 50, or 60 cycle electricity. No current flows twice during each cycle.

I'm done here. That's the best I can do.

What type of lamp? incandescent, mercury, halogen, fluorescent, sodium, neon, xenon, etc?

Are the blades spaced symmetrically?

50 Hz or 60 Hz doesn't matter, as long as they are the same for the light and the motor if the light is the correct type.

I would suggest that if you do not trust the answers that you have been given on this forum, ask the questions again elsewhere. Many attempts have been made to explain the answer by several very smart people. If that is not adequate perhaps an appropriately phrased question to Google would be a good start.

Good Luck, Old Salt

There is no need to get annoyed.

If you dont want to answer or if you think I am dumb enough to not understand your answer just unsubscribe yourself from the post.

PC-

When I posted that answer there was no annoyance involved. Caution- that may not hold true now!

First, would I have taken any time to compose and post the aforementioned answer if I was annoyed. Yes, my time is free to you but not to me. Would you prefer to pay me my minimum consulting fee of $600 per day with a minimum of 8 hours plus first class transportation? That minimum only applied to companies with personnel that are positive and cooperative. All checks from new or uncooperative (I just don't like them) clients are required to pass the bank before I do anything.

Does "What type of lamp? incandescent, mercury, halogen, fluorescent, sodium, neon, xenon, etc? sound like annoyance? No! its information you should have provided even before you considered posting your question. Good Questions produce good answers, bad questions produce bad answers!

Does "Are the blades spaced symmetrically?" sound like annoyance? Not to me but please see the above reply for an answer.

Does "50 Hz or 60 Hz doesn't matter, as long as they are the same for the light and the motor if the light is the correct type". sound like annoyance? Simply a statement for your benefit because it is very relevant to your question.

As for the next part, where a potential source was given if you are not satisfied with this forum, it was included to aid you in further pursuing an answer to your question since you seemed to be annoyed with this forum and the answers you were getting.

As to your last statement "If you dont want to answer or if you think I am dumb enough to not understand your answer just unsubscribe yourself from the post." The first part "If you dont want to answer or if you think I am dumb enough to not understand your answer" I did want to answer and I was hesitant to answer your latest, #15, but now know that I was the big dumb one for even thinking about giving you some information. I guess I may have joined someone else's club.

As for "just unsubscribe yourself from the post", I would now ever consider doing that at this time. Somehow I have this morbid feeling that the previous entries will continue and be even more humorous. I sometimes need a good laugh.

Also, consulting fee is now $1,000/day plus first class travel, only first class accommodations of my choice and gourmet meals for me and the wife.

Hopefully Google will help you more than I apparently have.

Good Luck, Old Salt

PC-

Unfortunately you took an answer that was given to enhance your seeking the information you appeared to want.

No hurt, I'm a human being and have had my share of ups and downs in my career and my life. You make no difference to me on a "hurt scale" just as many others have made no difference.

Not a big shot, just a guy who tries real hard to help others, more so when I'm not paid for it.

No, I don't understand why you annoyed. I gave you at least two answers that were intended to help you obtain the solution.

Your question was very ambiguous and sufficient information was not given. That's the reason for the questions.

You clearly indicated that you were not satisfied with the answers you were getting from this forum. I suggested an alternate source of preliminary information to you for use for the answer. Again, if you don't like it here go elsewhere.

The statements had everything to do with the technical discussion. You wanted technical information for a question with less than minimum information and you didn't like the technical answers.

As for "and please don't talk for others" I was attempting to provide you with the general consensus of the participants of this forum without having to take an official vote. That's why I will not be leaving, too many good people here who support each other in giving assistance to technical questions. Sorry you were so dissatisfied with our help.

Good Luck, Old Salt

PC-

Sorry you have taken several attempts to give you short but important guidance on how to ask questions, the better the question--->the better the answer, as offensive to your intelligence or some other factor. All attempts have been to help you, not annoy you. In your post #12. But, there is one doubt. Suppose the frequency of the electricity is 50 Hz and I see this dimming effect, then does that mean, the fan is rotating faster or slower compared to electricity frequency (3 blade fan). Replying to that I asked a question that all of this is dependent upon-- What type of lamp is it? A factor which all replies are dependent upon. Something that should have been stated in the original and/or subsequent questions.

If this is not the proper forum to discuss technical things, (of which all of my answers including this one have contained, where is the proper place? I am attempting to inform you that the better the question--->the better the answer.

Thank you for the complement the information contained in my answers. I hope you consider this answer another of those good ones.

In summation- I don't give up, I .....just.......... let .............. them ............... fade .................. away ................... on ....................... their .......................... own .....................................!

Good Luck, Old Salt